1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method of fabricating a semiconductor device including removing impurities from a silicon nitride layer.
2. Discussion of the Related Art
Semiconductor device fabrication includes processes for forming thin films such as a conductive layer or an insulating layer. Silicon nitride is commonly used in semiconductor fabrication. For example, a silicon nitride layer can be applied as a hard mask layer in patterning thin films by photolithography and anisotropic etching. In addition, silicon nitride can be used for a passivation layer, an oxidation barrier layer, an etch stop layer or a gate spacer of a MOS transistor.
The silicon nitride layer can be formed by a chemical vapor deposition (CVD) process using a reaction of dichlorosilane (DCS; SiCl2H2) gas and ammonia (NH3) gas. However, the CVD process using DCS gas as a silicon source requires that the silicon nitride layer be formed at a high temperature, e.g., 700° C. to 800° C. The high-temperature processing can cause abnormal diffusion of impurity ions in the semiconductor substrate, degrading device performance. Furthermore, the ammonium chloride (NH4Cl) generated as a reaction by-product corrodes the metal parts of a process chamber, resulting in metal contaminants on the semiconductor substrate. In semiconductor device fabrication, it is desirable that particles and contaminants be minimized.
A silicon nitride layer can be formed using BisTertiaryButylAminoSilane (BTBAS; C8H22N2Si) as a precursor. Since the silicon nitride layer can be formed at a lower temperature of about 600° C. using BTBAS, the problems caused by high-temperature processing can be avoided, and undesirable reaction by-products such as ammonium chloride can be prevented. Examples of methods of forming a silicon nitride layer using BTBAS are disclosed in U.S. Pat. Nos. 5,874,368 and 6,515,350.
However, BTBAS includes a large amount of carbon and hydrogen. As a result, the silicon nitride layer formed using BTBAS as a silicon precursor may contain a large amount of impurities in the form of carbon and hydrogen. In particular, the carbon impurities may deteriorate the dielectric characteristic of the silicon nitride layer. In the case that the silicon nitride layer formed using BTBAS is used as a gate spacer of a MOS transistor, the carbon impurities can penetrate into a gate insulating layer of the MOS transistor, deteriorating electrical characteristics of the device.